[BUILD] New FET/RACK Official Help Thread - Please read first post!

Help Support GroupDIY:

Deadly Mix

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Any idea where to start troubleshooting? Anyone?
I'm about to start it's pair tomorrow and I'd feel a lot better if I get the first one in order before I start the next.
 

Deadly Mix

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The power supply passed its test when I tested before the rest of the build. Knowing what measurements I should be getting at other test sites could be helpful though. I'll check that out.
 

JMan

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The power supply passed its test when I tested before the rest of the build. Knowing what measurements I should be getting at other test sites could be helpful though. I'll check that out.
I’m assuming you’ve already seen this page, but just in case you haven’t, it is very helpful.
 

Deadly Mix

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NO, somehow I think I must have glossed over it. Looks familiar but I haven't read it so maybe I saw it before it was relevant to me. I'll definitely be checking that out. Thanks.
 

Deadly Mix

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I’m assuming you’ve already seen this page, but just in case you haven’t, it is very helpful.
Interesting, the first thing it says is that, if your voltage is too low you probably have a problem with a transistor. The one thing I was worried about is the 2N3053 transistor. I seem to have burned the contact off while removing the one I messed up on (forgot the spacer) and wasn't sure it was going to work until I get it to my tech to repair the contact on the PCB.
 

Deadly Mix

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When I test the PSU, first step - Set the ground in the screw-hole of the case then touch the red probe to the base where the green grounding wire is attached. It says I should have a reading of less then 1ohm. I have 2.4ohm

The new one I started building, thinking I'll just do better this time and somewhere along the line I'll learn whats wrong with the first, has a reading of 2.1

Is this a resistor that isn't soldered well enough? A cap? What is going on?
 

JMan

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I wouldn't mess around too much until you figure that part out. What you're measuring there is the resistance on the path of your safety ground from the AC inlet, so you definitely want to make sure that's all squared away before you move on. Try probing around the area just a bit and see if that changes anything on your meter -- sometimes the connection is fine but maybe the probe is touching a bit of solder that increases the impedance reading slightly, or your black probe isn't actually in good contact with the chassis, something like that. At any rate, you do want to make sure that this path has as little resistance as possible since it is a very important one.
 

Deadly Mix

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I wouldn't mess around too much until you figure that part out. What you're measuring there is the resistance on the path of your safety ground from the AC inlet, so you definitely want to make sure that's all squared away before you move on. Try probing around the area just a bit and see if that changes anything on your meter -- sometimes the connection is fine but maybe the probe is touching a bit of solder that increases the impedance reading slightly, or your black probe isn't actually in good contact with the chassis, something like that. At any rate, you do want to make sure that this path has as little resistance as possible since it is a very important one.
Thanks for the tip.
I suspect I've been having an issue with the solder doing what its told to do because of a shitty iron. More accurately, 2 shitty irons and a station that doesnt display the accurate temp.
 

thelongramble

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Hello. I purchased a Rev F rack kit and appear to have been sent an incorrect part. I'm supposed to have a 7.68K resistor for R071 but didn't receive one. Instead, I appear to have gotten an extra 6.8K resistor. I've used my DMM and tested all of the resistors when doing my initial inventory, and then again to double-check.

Does anyone know if I can use the 6.8K instead at R071? I apologize if that's an ignorant question. I've put lots of kits together, but don't actually know much about the theory behind them. I reached out to Hairball, but have yet to hear back and I'd like to get this unit up and running for a big client project that starts in a few days. Thank you!
 

thelongramble

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I'm guessing after a week of hearing nothing here or from other places I've attempted to contact Hairball, that I'm unlikely to get any kind of response and should try and track down my own 7.68K resistor locally if I want to get this thing up and running?
 
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JMan

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It was a holiday in the US last week, plus businesses were gearing up for all of the Black Friday stuff, so it’s not surprising that you didn’t hear back from Hairball.

I don’t have an answer for you about substituting a different resistor value there, but you could certainly just order the correct value from Mouser. If you want to avoid the shipping cost (since you’re buying one 10¢ part), see if you have a local electronics store, or barring that, perhaps a computer store that sells parts for arduino.
 

thelongramble

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It was a holiday in the US last week, plus businesses were gearing up for all of the Black Friday stuff, so it’s not surprising that you didn’t hear back from Hairball.

I don’t have an answer for you about substituting a different resistor value there, but you could certainly just order the correct value from Mouser. If you want to avoid the shipping cost (since you’re buying one 10¢ part), see if you have a local electronics store, or barring that, perhaps a computer store that sells parts for arduino.
Will do. Thanks.
 

BruceARP

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You might experiment with another resistor in series with the 6.8 k to equal 7.68k
Try like a few 82ohm or something close.
In a pinch I have found just the right combination to make it work.
 

thelongramble

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By a few 82 ohm I mean grab a hand full of resistors close to that and measure them. You may be surprised you have the right combination.
Thank you for the help. I ended up ordering a few 7.68K resistors through a national distributor here in Canada. $1 for the parts and $20 for shipping, but what can you do? Need to get this thing up and running. Still no word from Hairball anywhere I've contacted them. Ah well.
 
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JMan

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You might experiment with another resistor in series with the 6.8 k to equal 7.68k
Try like a few 82ohm or something close.
In a pinch I have found just the right combination to make it work.
Just in case someone else comes along with a similar issue at some point, this should be 820 ohms and not 82. (This post is more directed at that future person, so BruceARP I hope you won’t read this as pedantic, I think you just missed a zero).

You would add the values of the two series resistors together to get the total resistance (6.8k + 820 gets you relatively close to the desired 7.68k in this case. If you happen to have an 887 ohm resistor on hand instead of the 820, all the better). This would hold true anywhere you need to use two smaller resistors in series to substitute for a single larger resistor value that you don’t have on hand. Definitely a useful trick when you need it!
 
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